A known vehicular braking apparatus for use in an automobile or the like is disclosed in, for example, Japanese Patent Application Laid-Open (kokai) Nos. 5-116607 and 10-264801 and has a shut-off valve for shutting off, as needed, a flow of oil, which serves as a working liquid, from a wheel cylinder to a master cylinder; a pressure increase-decrease control valve for increasing and decreasing the pressure in the wheel cylinder; a reservoir for receiving and storing oil from the wheel cylinder in a reservoir chamber when the pressure increase-decrease control valve is in a pressure decrease position; a pump, which serves as pressurizing supply means, for sucking in and pressurizing oil from the reservoir chamber and supplying oil to the wheel cylinder via the pressure increase-decrease control valve when the pressure increase-decrease control valve is in a pressure increase position; and a communication control valve for controlling communication between the master cylinder and the reservoir chamber.
In a braking apparatus of this type, in an ordinary braking mode, the pressure in the master cylinder is introduced into the wheel cylinder via the shut-off valve, thereby increasing and decreasing the pressure in the wheel cylinder by means of the pressure in the master cylinder. In a braking mode in which the pressure in the wheel cylinder must be made higher than the pressure in the master cylinder, the shut-off valve shuts off a flow of oil from the wheel cylinder to the master cylinder, and the pump is driven. High-pressure oil supplied from the pump is supplied to or drained from the wheel cylinder by means of the pressure increase-decrease control valve, thereby controlling the pressure in the wheel cylinder to a desired level.
According to a braking apparatus of this type, the communication control valve automatically opens and closes according to the pressure in the master cylinder and the suction pressure of the pump, thereby functioning as a pressure regulating valve for automatically regulating the pressure in the reservoir chamber according to the pressure in the master cylinder and the suction pressure of the pump. Therefore, as compared with the case where the communication valve is a solenoid valve, and also the solenoid valve is controlled on the basis of the results of detection by various sensors, the cost of the braking apparatus can be lowered, and control of the braking apparatus can be simplified through reduction of elements-to-be-controlled of the braking apparatus.
In the conventional braking apparatus as disclosed in the above-mentioned publications, the communication control valve is a normally-opened check valve. At the time of nonbraking when a driver does not perform a braking operation, in the check valve, a valve element is moved away from a valve seat. Therefore, at the time of nonbraking, the master cylinder and the reservoir chamber communicate with each other. When the driver begins a braking operation with a resultant increase in the pressure in the master cylinder, a flow of oil caused by a differential pressure between the pressure in the master cylinder and the pressure in the reservoir chamber causes the valve element of the check valve to be seated on the valve seat. Thus, the check valve closes, thereby shutting off communication between the master cylinder and the reservoir chamber.
However, since the check valve which serves as the communication control valve is a normally-opened check valve, even when the driver begins a braking operation, the check valve does not close until the amount of oil in the reservoir chamber increases so that the reservoir piston moves to a position of allowing the check valve to close and until a differential pressure between the pressure in the master cylinder and the pressure in the reservoir chamber attains a predetermined value. Accordingly, a portion of oil in the master cylinder unavoidably flows into the reservoir chamber via the check valve. Therefore, as compared with the case where all of oil flowing out from the master cylinder is supplied to the wheel cylinder via the shut-off valve, pressure rise in the wheel cylinder is delayed. This unavoidably raises a problem of deterioration in feeling which is caused by delay in pressure rise in the wheel cylinder and delay in actual braking action when the braking operation is performed. There is room for improvement in terms of enhancement of braking response at the time of beginning of the braking operation by the driver.
In the braking apparatus disclosed in the above-mentioned Japanese Patent Application Laid-Open (kokai) No. 10-264801, a pin (24) which butts against a ball (23b) of a check valve (23) is displaceable in relation to a piston (16b) of a reservoir in the opening/closing direction of the check valve. However, the check valve (23) is a normally-opened valve, and the pin (24) is not displaced in relation to the piston (16b) except for the case of manual movement for maintenance; i.e., the pin (24) does not automatically move in relation to piston (16b) in the valve-opening direction according to the suction pressure of a pump. Therefore, the braking apparatus disclosed in the above-mentioned Japanese Patent Application Laid-Open (kokai) No. 10-264801 also involves the above-mentioned drawbacks.